Amorphous solids have irregular arrangement of atoms and molecules, with short range order. They are characterised as isotropic, that is, because of their irregular arrangement, the refractive index is the same in all directions when measured. Amorphous solids also do not have a defined heat of fusion because they do not have a sharp melting point. They also can soften over a long range of temperatures so they are known as supercooled liquids. Quartz glass is a very pure form of amorphous silica, as it does not contain any impurities added to normal glass in order to lower its melting temperature. Being amorphous, it does not have a defined crystalline structure, so option (i) is a feature not shown by quartz glass.

Quartz glass’ refractive index is not zero and same in all directions. Option (ii) is a feature of quartz glass.

Because it is amorphous, it does not have a fixed melting point and no definite heat of fusion. Option (iii) is not a feature of quartz glass.

As amorphous solids are also known as supercooled liquid, Option (iv) is a feature of quartz glass.

Thus, option (i), (iii) are the correct option.